detect illegal pointer comparisons and pointers modified too far outside their base object

main.leg

@@ -1,6 +1,6 @@
 # main.leg -- C parser + interpreter
 #
-# Last edited: 2025-02-05 13:53:41 by piumarta on xubuntu
+# Last edited: 2025-03-21 11:45:50 by piumarta on m1mbp.local
 
 %{
 ;
@@ -2262,20 +2262,6 @@ cvt_t converter(int tfrom, int tto)
     return converters[tto - Tvoid][tfrom - Tvoid];
 }
 
-oop incr(oop val, int amount)
-{
-    switch (getType(val)) {
-	case Integer:	return newInteger(integerValue(val) + amount);
-	case Float:	return newFloat  (  floatValue(val) + amount);
-	case Pointer:	return newPointer(get(val, Pointer,type),
-					  get(val, Pointer,base),
-					  get(val, Pointer,offset) + amount);
-	default:
-	    fatal("cannot increment: %s", toString(val));
-    }
-    return nil;
-}
-
 int isType(oop obj)
 {
     type_t type = getType(obj);
@@ -2315,6 +2301,38 @@ int typeSize(oop type)
     return 0;
 }
 
+oop incr(oop val, int amount)
+{
+  switch (getType(val)) {
+    case Integer:	return newInteger(integerValue(val) + amount);
+    case Float:	return newFloat  (  floatValue(val) + amount);
+    case Pointer: {
+      oop t = get(val, Pointer,type);
+      oop b = get(val, Pointer,base);
+      int o = get(val, Pointer,offset) + amount;
+      oop p = newPointer(t, b, o);
+      switch (getType(b)) {
+	case Variable:
+	  if (o < -1 || o > 1) fatal("pointer modified beyond base object: %s", toString(p));
+	  break;
+	case Memory: {
+	  int limit = get(b, Memory,size) / typeSize(get(t, Tpointer,target));
+	  if (o < -1 || o > limit) fatal("pointer modified beyond base object: %s", toString(p));
+	  break;
+	}
+	default:
+	  println(b);
+	  assert(!"unimplemented");
+	  break;
+      }
+      return p;
+    }
+    default:
+      fatal("cannot increment: %s", toString(val));
+  }
+  return nil;
+}
+
 int toBoolean(oop arg)
 {
     switch (getType(arg)) {
@@ -3459,7 +3477,11 @@ int compare(oop a, oop b)
 	    case Float:		return CMP(  _floatValue(a),   _floatValue(b));
 	    case Pointer: {
 		oop ba = get(a, Pointer,base),   bb = get(b, Pointer,base);
-		if (ba != bb) return CMP((intptr_t)ba, (intptr_t)bb);
+		// BUG -- this should report an illegal comparison
+		if (ba != bb) {
+		  fatal("illegal comparison between pointers to different objects: %s and %s\n", toString(a), toString(b));
+		  return CMP((intptr_t)ba, (intptr_t)bb);
+		}
 		int oa = get(a, Pointer,offset), ob = get(b, Pointer,offset);
 		return CMP(oa, ob);
 	    }